The first peripheral to use Bluetooth technology will be a wireless headset. According to Ericsson's schedule, this earphone for Ericsson T28 telephone came out in July 2000. The corresponding products of Nokia and Motorola will wait until late 2000. At that time, as long as you add an accessory using Bluetooth technology to the mobile phone and place the headset in your ear, you can put the mobile phone in your pocket, free your hands during a call, and even just press a button on the headset to answer the call. Moreover, due to the voice recognition function of Ericsson T28, you can make some commonly used calls just by saying the person's name. Another selling point of the headset is that because the transmission level of Bluetooth headset is far lower than that of ordinary mobile phone headset, manufacturers will have the opportunity to vigorously render its advantages to human health.
However, the positioning of Bluetooth is low-power, short-range wireless transmission, and there is still a huge application space in consumer electronics in the future. It will take personal portable products such as mobile phones and PDAs as its largest application market. According to in stat estimates, by 2005, mobile phones will account for 71% of all Bluetooth application products, followed by personal computers and PC cards, accounting for 14% and headphones accounting for 6%. Analysts pointed out that with the progress of Bluetooth technology and the decline of chipset cost, Bluetooth and Wi Fi will still account for half of the short-range wireless communication market respectively.
Compared with the special miniature invisible wireless earphones, civil and industrial wireless earphones can be described as a variety. But in fact, if this kind of earphone is not very special in terms of communication and electronics, it is more likely to involve the discussion in the field of acoustics.
For this kind of earphone, the whole system can be analyzed with reference to low-power simplex or duplex radio communication system. Generally pay attention to restore the fidelity of sound quality, with exquisite appearance and pleasing; In contrast, due to environmental reasons, industrial wireless headphones are designed with more emphasis on reliable performance.
In the circuit, high-grade products generally integrate analog or digital compression technology in the processing mode of transmission process, and the modulation modes adopted are also diverse, such as RF, infrared, pure audio induction, etc. Varieties adopting RF mode and products using ultra-high frequency band or Bluetooth Technology (900mhz-2.4ghz, etc.) can relatively obtain more ideal technical indicators and meet the requirements of green environmental protection, which actually represents an important development direction in this field.
As shown in the figure, this full duplex wireless headset for radio and television broadcasting adopts low-power FSK audio digital compression, decompression and modulation processing technology, which has high reduction index and anti-interference performance in the range of 20Hz-20KHz of human audible audio. The whole works at 863mhz in UHF band. PLL phase-locked loop makes it have stable RF performance. In general, the reliable communication distance is greater than 150m.
Generally, in order to achieve ideal high-speed digital speech compression transmission effect, large RF bandwidth or advanced modulation technology are generally required. In order to reduce the transmission rate of digital speech signal, adaptive audio pulse coding (ADPCM) or continuously variable slope incremental modulation (CVSD) are often used to process the signal. These schemes are based on differential coding. The basic concept is to send the difference between the current sample and the previous sample instead of the absolute value obtained by sending the sample.
Wireless headphones will be used in many occasions. In addition to radio and television systems, such as call center, audio-visual teaching, home hifi, hands-free communication personal mobile phone (Bluetooth headset), "silent conference", interview and investigation, tourism and other wireless headphone systems can show their style and are gradually becoming a trend. In fact, there is no great difference in the basic structure or circuit principle between various wireless headphones, and it is not necessary to strictly divide them into several categories. On the contrary, many headphones are used in a wide range of industries. When it comes to differences, they are only for applications in different occasions. The parameters and costs of the system have a certain trade-off bias, which is the same as the requirements of special micro wireless headphone system.